Inorg. Chem. 1990, 29, 4584-4586
4584
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where H3,reported further upfield from H4, and H5, triplets. The downfield shift observed for H3, in the bimetallic cyanoiron(I1) complex must be due to increased a-withdrawing effects of the CN- vs tpy ligand on the metal center. The monometallic complex displays four sets of doublets and four sets of triplets, as expected from protons on the coordinated and noncoordinated rings. Two sets of doublets at 8.82 and 8.74 ppm are assigned to the protons in the coordinated rings as H6,and H3,. Doublets at 8.04 and 6.98 ppm are assigned to H6 and H3 on the uncoordinated rings. As previously noted for the monometallic ruthenium complex,23when the coordinated pyridine and diazine rings are held coplanar, the uncoordinated pyridine ring presumedly rotates out of plane, resulting in an upfield shift of the uncoordinated protons. The observation of H3 in the [Fe(CN)3(tpd)]- complex to be shifted upfield to 6.98 ppm appears to support the previous rationale. Acknowledgment. We acknowledge the generous financial support of this work through a Bristol-Myers Co. Grant of the Research Corp. R.R.R. thanks Jeff Boone at the Frank Seiler Laboratories, USAFA, Colorado Springs, CO, for N M R data.
16.0{
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0.80
0.90
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parameter
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Contribution from the Department of Chemistry, Georgetown University, Washington, D.C. 20057
Reformulation of the HexafluorooctadecatungstateAnion as a Heteropoly Sodate Complex: [H,F,NaW,,OSJ'Thomas L. Jorris, Mariusz Kozik,; and Louis C. W. Baker* 1
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Gutmann AN Figure 3. Plots of umsl (kK = lo3 cm-I) for the lowest energy MLCT peak of [Fe(CN),(tpd)]- (m) and [(Fe(CN),),(tpd)12-(A)ions in various solvents vs (a) E*MLCT solvent parameter and (b) Gutmann AN.
of the lowest energy MLCT peaks for [(Fe(CN)3),,2(tpd)]-,2-vs the E * M L C T solvent parameter^^^ for combined alcoholic and aliphatic solvents are nonlinear (Figure 3a). Separation of solvents produces two distinct linear solvatochromic behaviors for both mono- and bimetallic complexes. The discontinuity of [Fe(CN),(tpd)]- and [(Fe(CN),),(tpd)Jz- plots may result from the fact that the E * M L C T solvent parameter was derived from solvent effects on neutral complexes and does not compensate for enhanced ground-state stabilization due to the polarizability of anionic metal complexes by the very polarizing alcoholic protons. The Gutmann acceptor number, a solvent parameter based on the hardness of the solvent in donor-acceptor interaction^,^' appears to be a more appropriate model for the [(Fe(CN)3)l,2(tpd)J--2-complexes. A plot of urnaxMLCT vs Gutmann AN (Figure 3b) is linear, suggesting that molecular polarizability of the metal complex plays an important role in solvatochromic behavior.32 Proton NMR spectra of [(Fe(CN)3),,2(tpd)]-v2-were recorded in D 2 0 (Table 111). The bimetallic complex spectrum shows two doublets and two triplets, as expected from the symmetrically coordinated tpd ligand. The two sets farthest downfield at 8.95 and 8.66 ppm are doublets that must be assigned to H6, and H3, on coordinated pyridine rings. In accordance with previous assignments for cyanoiron( 11) complexation to pyridine,33and tpd when symmetrically coordinated to two metals,24the doublet at 8.95 ppm is assigned to H6, and the 8.66 ppm doublet to Hy.The triplets at 7.92 and 7.54 ppm are assigned to H., and H5,, respectively, also in agreement with previous assignments. It is of interest to note that, for the [(Fe(CN),),(tpd)I2- ion, the H3, doublet is shifted downfield with respect to the H4, and H5,triplets, in contrast with the previously reported [ ( R ~ ( t p y ) ) ~ ( t p d )ion, ]~+ (30) Manuta, D. M.; Lees, A. J. Inorg. Chem. 1983, 22, 3825. ( 3 1 ) Gutmann, V. The Donor-Acceptor Approach to Molecular Interactions; Plenum . .. ..-... Press: ... . .. New . .
...
York. 1978. .. . .. . . (32) Kaim, W.; Kohlmann, S. Inorg. Chem. 1986, 25, 3306. (33) Malin, J. M.; Schmidt, C. F.: Toma, H. E. Inorg. Chem. 1975, 14, 2924.
0020- 1669/90/ 1329-4584$02.50/0
Receiced June 5, 1990
Chauveau, Doppelt, Lefebvre, et al.'-'' published an elegant and valuable series of papers (1974-1983) on fluoroisopolytungstate complexes, chiefly derivatives of the metatungstate ( [H2WI2O4J6)structure, wherein F ions replaced various interior isoelectronic 02-ions. In the course of that work they reported4 the preparation and structure of "[H2F6W18056]s--,which is grossly isostructural with the well-known Well~-Dawson'~-'~ species (r-[P2w18062]6- but wherein the P atoms have been replaced by H's and the six most central 0 atoms have been replaced by F atoms. Their structure proof was based on chemical analyses, similarities of X-ray powder patterns and CV data with those of known Wells-Dawson derivatives, ultracentrifugation, and especially 'H and I9F N M R spectroscopy. The present paper modifies their conclusion by showing that a nonexchanging Na+ ion is enclosed at the very center of the complex, in trigonal-prismatic coordination to its six nearestneighbor F atoms. (See Figure 1.) So far as we are aware, this is the first case of trigonal-prismatic coordination by hard ligands. We have been unable to form the complex in the absence of Na+. In 1973 our laboratory reported15 the first polytungstate complexes containing fluoride ions substituted for oxide ions. We subsequently unequivocally established'6'8 those complexes and others as comprising a series of isomorphous heteropoly d,l-alaquometalloheptadecatungstopolyfluorosodates, d , l - a , [(H20)M"+05H2F6NaWl,050]("-n)-, wherein M"+ = Co2+,Co3+, Zn2+,Ni2+, Mn2+, or Mn3+. The detailed structure proof was based primarily on 23Na, 19F, 'H, and ls3W N M R spectroscopy, a complete X-ray structure, and isotope-exchange studies. That proof is contained in a dissertation16 and has been presented at an international heteropoly symposium.ls It will be the subject of a forthcoming detailed major paper. The 18-tungstohexafluorosodate complex which is the subject of this paper turned out to be an isomorph of the a,-aquometalloheptadecatungsto'Abstracted from a portion of the Ph.D. dissertation of Thomas L. Jorris, Georgetown University, 1987. Present address: Department of Chemistry, Canisius College, Buffalo, NY.
0 1990 American Chemical Society
Notes
Inorganic Chemistry, Vol. 29, No. 22, 1990 4585
150 160 P PM Figure 2. la3WN M R spectrum of Li7[H2F6NaW18056] solution in D20. Standard frequency = 12.505 MHz; no. of scans = 2065; sweep width I40
= 830.6 Hz.
polyfluorosodates. Therefore t h e X-ray results, Z3Na NMR spectroscopy, a n d 22Na-exchange studies on those heteropoly species substantiate and confirm t h e present report.
Experimental Section Preparation and Purification. Preparation of the potassium salt of the 6-fluoro- I 8-tungsto complex was fundamentally by the method worked out by the French authors., An aqueous mixture of H F and HCI solutions is heated with a solution of Na2W04. The mixture is cooled and filtered, and more of the two halogen acids is added. A Drechsel ether Chauveau, F.; Souchay, P. J . Inorg. Nucl. Chem. 1974, 36, 1761. Launay, J.-P.; Boyer, M.; Chauveau, F. J . Inorg. Nucl. Chem. 1976, 38, 243. Chauveau, F.; Doppelt, P.; Lefebvre, J. J . Chem. Res., Synop. 1978, 130; J . Chem. Res. Miniprint 1978, 1727. Chauveau, F.; Doppelt, P.; Lefebvre, J. Inorg. Chem. 1980, 19, 2803. Chauveau, F.; Doppelt, P.; Lefebvre, J. J . Chem. Res., Synop. 1981, 155; J . Chem. Res., Miniprint 1981, 1937. Doppelt, P.; Lefebvre, J. Nouo. J . Chim. 1981, 5, 463. Lefebvre, J.; Chauveau, F.; Doppelt, P.; Brevard, C. J . Am. Chem. Soc. 1981, 103. 4589. Chauveau, F.;Doppelt, P.; Lefebvre, J. Polyhedron 1982, I , 263. Sanchez, C.; Livage, J.; Doppelt, P.; Chauveau, F.; Lefebvre, J. J . Chem. SOC.,Dalron Trans. 1982, 2439. Chauveau, F.;Doppelt, P.; Lefebvre, J. Bull. Soc. Chim. Fr. 1983, 197. Chauveau, F. Bull. Soc. Chim. Fr. 1986, 199. Wells, A. F. Slrucrural Inorganic Chemistry, 1st ed.;Oxford University Press: Oxford, U.K., 1945; p 344. Dawson, B. Acta Crysrallogr. 1953, 6, 1 13. DAmour, H. Acta Crystallogr.,Sect. E.: Struct. Crystaffogr.Crysr. Chem. 1976, 832, 729. Baker, L. C. W. Proc. Int. Conf. Coord. Chem. 15th 1973 (portion of plenary lecture, on work by L. C. W. Baker and I. Todorut). Jorris, T. L. Doctoral Dissertation, Georgetown University, 1987. Marcu, Gh.; Ciogolas, 1.; Todorut, 1. Rev. Roum. Chim. 1979, 24, 715. Baker, L. C. W.; Jorris, T. L.; Todorut, 1.; Jameson, G. B. Abstracts of Papers presenred at the Symposium on Heteropolyanions and Their Caralyric Properties, Third Chemical Congress of the North American Continent, Toronto, 1988.
extraction at 0 OC gives an ether solution from which the free acid of the complex crystallizes upon evaporation. It is recrystallized three or four times from water. Addition of concentrated KCI or N(CH,),Cl solution to a solution of recrystallized free acid precipitates the potassium or tetramethylammonium salt of the complex. These products were nor recrystallized in the original work. Our I9FN M R spectrum of the four-times-recrystallized free acid in DzO shows primarily the single intense peak reported earlier,, but our spectrum covers a moderately broader chemical shift range than that originally shown4 and clearly reveals a number of lines (collectively of substantial intensity) attributable to one or more impurities. Recrystallization of the precipitated potassium salt results in separation of a white crystalline impurity from the crystals of the desired light greenish product. The white crystals comprise about 10%of the product. Impurities could still be detected in a D 2 0 solution of the once-recrystallized light green crystals by use of high amplification of the I9F N M R spectrum. Further recrystallization of the greenish product was necessary to obtain pure material showing only the single resonance. Since the Li salt of the complex is more soluble than the other salts mentioned, all the N M R spectra discussed below were obtained with solutions of the Li salt, prepared by metathesis from a solution of the purified K salt by addition of a 2-fold excess of LiC104. All N M R spectra were obtained on a Bruker AM300 WB N M R spectrometer. Although it has been s u g g e ~ t e dthat ’ ~ NaBr solutions be used as the chemical shift standard for 23Na N M R spectroscopy, other studies20*21 have shown that considerable effects of solvent, concentration, and anion on chemical shift were most pronounced in the cases of large anions such as 1- and Br-. These studies showed that the 23Na N M R chemical shifts for solutions of NaC10, in DzO were least subject to these variations. Accordingly, the 23Na N M R spectra of the polyfluoropolytungstate complexes were recorded in DzO by the sample replacement method with 2 M NaCIO, in DzOas the external chemical shift reference standard.
Results and Discussion T h e above-described evidence of impurities accounts for t h e incorrect analyses in t h e original paper: which appeared t o show 8.0 H+ or K+ or N(CH,),+ per 18 W atoms. The same incorrect proportion of cations had probably carried through from impurities in t h e free acid. IS3WNMR Spectroscopy. Our 183WNMR spectrum (Figure 2) is consistent with t h e spectrum described by Chauveau in t h e text of her 1986 review,” but the spectrum shown for this complex in t h a t review (Figure 8) was evidently accidentally replaced by the spectrum of a different compound. Our Is3W NMR spectrum exhibits a s h a r p ( A U ~
